The present invention relates to an electrostatic deflecting electrode unit for use in a charged beam lithography apparatus and a method of manufacture the same.
This application is based on Japanese Patent Application No. 9-64935, filed Mar. 18, 1997, the content of which is incorporated herein by reference.
As is well known, in the process of manufacturing semiconductor devices lithography techniques are used to transfer a mask pattern drawn on a mask made of quartz to a wafer. In general, a charged beam lithography apparatus is used to form a mask pattern on a mask. In the charged beam lithography apparatus, a beam of electrons emitted from an electron gun is shaped into a sharp narrow beam having a desired shape in vacuum atmosphere and the shaped electron beam is then irradiated and deflected repetitively in accordance with pattern data to form a pattern on the mask.
Recently, the pattern density of semiconductor devices has increased rapidly and correspondingly the critical dimension of mask patterns used in lithography has also been further scaled down. In order to form a very small pattern in as short a time as possible, therefore, the lithography apparatus must conform to high throughput and high accuracy requirements.
The lithography apparatus is usually equipped with an in-lens electrostatic deflecting electrode unit that is built into an electric optical lens. There is a need to scale down the dimensions of the deflecting electrode unit. In addition, in order to obtain desired deflection sensitivity and electric optical characteristics, high-precision parts processing is required.
When used for a long time, the surface of the electrostatic deflecting electrode is contaminated due to scattering of a phosensitive resist applied to a mask for drawing a pattern thereon. When a nonconductive contaminant such as a photosensitive resist is attached to the surface of the electrostatic deflecting electrode, charged-up which is a cause of electron beam drift is caused, thus making it impossible to maintain desired patterning precision. In such a case, the electrostatic deflecting electrode unit needs to be replaced with a new one. Therefore, there is a demand for development of a method of manufacturing electrostatic deflecting electrode unit of the same dimension and the same performance efficiently with precision. This is for the purpose of preventing the patterning precision from reducing because of deflecting electrode unit replacement.
Referring now to FIG. 1, there is illustrated a schematic of an electron beam lithography apparatus which is one of conventional charged beam lithography apparatuses.
An electron beam 2, which is a charged beam, produced by an electron gun 1 passes through a condenser lens 3, a first shaping aperture 4, and a projection lens 5 in sequence and then passes through a second shaping aperture 6, whereby it is shaped in cross-section. The shaped electron beam projected through an objective lens 8 for reducing the beam size onto a substrate 9 which is maintained at ground potential.
The projection lens 5 consists of two lens elements. The projection lens 5 has a shaping deflecting electrode unit 10 placed inside its lens elements, while the objective lens 8 has an objective deflecting electrode unit 11 placed inside thereof. The deflecting electrode units 10 and 11 have deflecting electrodes 12a through 12h and 13a through 13h, respectively. In the arrangement of these deflecting electrodes, a pair of electrodes which face each other is used as a base unit, and N (N is an integer of 2 or more) pairs of such electrodes are placed around a center axis. A driving voltage is applied between the electrodes in each pair, so that electric fields are generated in the space surrounded with the electrodes.
The electron beam 2 passes through the electric fields, then is projected onto the substrate 9. The electron beam 2 can therefore be deflected by changing the driving voltage between the paired electrodes of the two vertically placed sets of the deflecting electrodes 12a through 12h and 13a through 13h. By changing each driving voltage, the amount of deflection can be controlled to draw a desired pattern 14 on the substrate 9.
In order to improve the accuracy of the pattern 14, it is required to improve the accuracy of the deflection of the electron beam 2. To this end, it is required to make the electric fields in the spaces surrounded with the deflecting electrodes uniform so as to prevent some variation in the electronic beam position from affecting the angle of deflection of the electron beam.
One of methods that meet such requirements is to make the spacing between the faced deflecting electrodes in each pair large and confirm whether the deflecting electrodes are precisely manufactured. When the spacing between the faced deflecting electrodes is set large, however, it is required to apply a high driving voltage between the paired deflecting electrodes in order to achieve electric field strength necessary to deflect the electron beam by a predetermined amount. In general, a deflection amplifier that generates the driving voltage has a drawback that its response speed decreases with increasing output voltage. With this method, therefore, at present it is difficult to make fast response and high precision stand together.
On the other hand, another method has also been conceived which prevents the response speed of the deflection amplifier from lowering in order to achieve fast response by making the spacing between the deflecting electrodes small and thereby allowing the driving voltage to be low. A still another method has also been conceived which achieves high-precision resolution by subdividing each deflecting electrode to increase the number of the deflecting electrodes and setting the driving voltage for each electrode pair finely to generate a uniform electric field.
According to the above two methods, however, since the dimensions of individual parts are scaled down, the dimensional precision of each deflecting electrode must be increased accordingly. However, it is difficult to increase the dimensional precision. There is another drawback that a deflection distortion of the electron beam 2 is increased due to a decrease in assembly precision.
On the other hand, there is known an example of a deflecting electrode unit which removes the above-described drawback by improving the precision of the subdivided small deflecting electrodes. This type of deflecting electrode unit is shown in FIG. 2.
With this deflecting electrode unit, each of eight T-shaped electrodes 20 is attached to a respective one of insulating members 21 machined so that their thickness becomes uniform and then removably fixed with screws to a deflecting electrode holder 22 of octangle prism-machined with precision with an NC machine. At the time of assembly, after the insulating member 21 is coupled to the upper portion of the T-shaped electrode 20 with screws, a determination is made as to whether or not the surface of the T-shaped electrode 20 that faces the holder 22, the surface 21a of the insulating member 21 that is to be attached to the holder 22 and the opposite surface 21b each have desired dimensional precision, flatness, and parallelism. After the desired precision has been confirmed, the insulating member 21 attached with the T-shaped electrode 20 is secured to the holder 22 with reference to the end surface of the insulating member and the abutting portion (not shown) of the holder 22.
Since the surface of the insulating member 21 for insulatingly separating the electrodes is manufactured with high precision, the precision of the deflecting electrode unit can be theoretically maintained at high level if there is no error in manufacturing process.
Further, there are other conventional deflecting electrode manufacturing methods described in Japanese Patent Disclosures Nos. 2-123651 and 5-29201 and an easy-to-manufacture deflecting electrode described in Japanese Patent Disclosure No. 5-129193.
With the conventional deflecting electrodes for use in charged beam lithography apparatus including an apparatus shown in FIG. 2, the positional precision of the electrode surfaces cannot be confirmed after assembly. Therefore, the precision in the assembly of each part is required stringently (particularly the precision in the attachment of the insulating member 21 to the holder member 22) and moreover parts must be selected so as to minimize variations during assembly. Considerable labor will be involved in evaluating the precision of parts and selecting good parts.
In the manufacturing method described in Japanese Patent Disclosure No. 2-123651, conductive silicon carbide SiC of hollow symmetric form finished as a cylindrical part having a roundness of the order of some tens of microns by lathe machining after baking and an insulating material, such as alumina-based ceramic, of hollow symmetric form which is patterned with wiring are made integral with each other by fitting an end portion of one into the other. Then, grooves are formed in the silicon carbide, serving as an electrode member, to the depth to reach the alumina-based ceramic at the fitted portion, thereby dividing the silicon carbide into a predetermined number of pieces. Thus, high-precision deflecting electrode unit is obtained.
With this method, however, since one end of the electrodes is fitted into the insulating material, there is the possibility that the positional precision of each electrode cannot be maintained after the electrode member has been cut. Additionally, it is difficult for the deflecting electrode unit with an assembly accuracy on the order of some tens of microns resulting from the fitting structure to satisfy electron beam positional precision requirements for patterning on submicron levels as in recent years because of its too large deflection abbreviation.
In the manufacturing method described in Japanese Patent Disclosure No. 5-29201, a cylindrical block made of metal is formed with a central hole through which an electron beam will pass, then a plurality of inter grooves are formed radially in its inside surface and an equal number of outer grooves are formed radially in the outside surface. After that, an insulator is inserted into each of the outer grooves and then glued to the metal. Subsequent to gluing, each inter groove is further cut to eventually connect with the corresponding outer groove, thereby forming a deflecting electrode unit.
In this method, subsequent to gluing, baking is performed after cleaning to remove chips formed in joining the inter and outer grooves and oil. In baking, there is the possibility that desired precision may not be obtained due to thermal deformation resulting from the difference in thermal expansion between the electrode made of metal and the insulator serving as glue.
The deflecting electrode unit disclosed in Japanese Patent Disclosure No. 5-129193 has a structure such that each of deflecting electrodes is secured with screws to the internal surface of a tube-like insulator made of ceramics. That is, electrodes in the form of cylinder having the same diameter as the inside diameter of the tube-like insulator are fitted into the insulator and then a hole is bored in the center of the electrode along the height of the cylinder. Positioning-pin holes and threaded holes are then formed from the outside of the insulator. The electrode and the insulator are fixed in position with positioning pins and screws. The hole of the electrode is polished inside so that its cross-sectional shape becomes a circle of a predetermined size. Subsequent to polishing, the electrode is split by means of electric discharge machining to obtain electrically isolated electrodes. After that, each deflecting electrode is taken off the insulator. The surface of each electrode subjected to electric discharge machining is finished by polishing. After polishing, each electrode is positioned by the positioning pin and then secured to the insulator with screws as it was prior to disassembly.
However, in the case where the cylindrical metal is fitted into the tube-like insulator member and then attached removably to the insulator with screws, the fitting may become loosened at the time of splitting the electrode member, or looseness may occur between the insulator and the electrode because of expansion due to heat generated at the time of machining and subsequent contraction. In such a case, retightening of screws may be required after the splitting of the electrode, and the electrodes may not be assembled with precision.
As described above, various electrostatic deflecting electrode units for use in the charged beam lithography system have been proposed heretofore. However, every deflecting electrode unit, while having advantages, is difficult to assemble with high dimensional precision.